In the Progress Report, we have shown that valinomycin (in the presence of K ion) at a concentration that brings about K ion conductance increase by several orders of magnitude, caused no change in K permeability in frog eggs and frog muscles. We shall extend these studies by including another ionophore, monactin, and other types of cells (e.g., human red cells). We shall also continue to wind up our intensive study of the Donnan theory of membrane equilibrium; evidence already overwhelmingly shows that it is theoretically faulty, and experimentally refuted. Our major efforts will be direct (1) further understanding of the electrical potential of the living cells with emphasis on testing the new equation presented a year earlier, (2) further understanding of the osmotic behavior of polymer-oriented water as a model of the living cell, (3) the identifications of the proteins in red (erythrocytes) ghosts responsible for selective K ion adsorption and weak Na exclusion, and the role of ATP in these manifestations, not seen in intact white ghosts.